Experiments will be undertaken to elucidate further why the transplantable reticulum cell sarcomas (RCS) in SJL/J mice and the B-cell lyphoma (PU5) in BALB/c mice grow in normal but not in total body gamma-irradiated syngeneic mice. The host-tumor relationship for these B lymphomas will be scrutinzed in detail. We will examine the nature of the antigen on the surface of RCS cells that induces a strong proliferative response in normal SJL/J T cells and further characterize, as to the number and T cell subset, the responding cells to this antigen. Their role in the generation of cytotoxic cells to RCS, which in contrast to the proliferative response is very low in the syngeneic SJL/J system, will also be determined. In order to characterize these further, a number of lymphoid cell, reticulum cell, and macrophage tissue culture cell lines as well as transplantable tumor cell lines will be examined for their ability to synthesize various serum proteins in vitro using the technique of autoradiography of immunoelectrophoretic patterns. This technique will also be applied to the study of sites of synthesis of group specific proteins of tumor virus (ALV-gs) in an analysis of the natural development of avian leukosis in sensitive chickens infected within 2 days after hatching. BIBLIOGRAPHIC REFERENCES: Carswell, E.A., Lerman, S.P., and Thorbecke, G.J. Properties of reticulum cell sarcomas in SJL/J mice. II. Fate of labeled tumor cells in normal and irradiated syngeneic mice. Cell. Immunol. 23:39-52, 1976. Lerman, S.P., Carswell, E.A., Chapman, J., and Thorbecke, G.J. Properties of reticulum cell sarcomas in SHL/J mice. Promotion of tumor growth in irradiated mice by normal lymphoid cells. Cell. Immunol. 23:53-67, 1976.